The present invention relates to a pigment-dispersion photo-sensitive coating solution for forming a colored image (also called a picture element) employed in color liquid crystal displays or image pickup devices and a method for preparation thereof as well as to a method for forming a colored image using the same. More particularly, the invention relates to a pigment-dispersion photo-sensitive coating solution and a method for preparation thereof, which provide a coating film of uniform thickness and excellent surface roughness and are capable of forming a colored image excellent in transmittance and contrast. The invention also relates to a method of forming a colored image for a color filter by using the pigment-dispersion photo-sensitive coating solution.
The color filter in a color liquid crystal display, image pickup device or the like is normally produced by forming colored images of red, green and blue on a substrate such as glass substrate, film substrate, silicon wafer or the like. Typically, a black matrix is provided for blocking light leakage from these colored images. A method of forming the respective colored images includes the steps of: uniformly applying a photo-sensitive coating solution containing a pigment dispersion of each corresponding color by a spin coater on a substrate on which a pattern of a light blocking layer was formed; baking (prebaking) the solution to give a dry coating film; patterning the resultant coating film by light exposure and developing a colored image; and thermosetting (postbaking) the resultant image. The procedure is repeated for each of the colors required by the color filter whereby the colored images of the respective colors are obtained. In some cases, a photo-sensitive coating solution containing a black pigment may be used for forming the black matrix.
To form a red-colored image, C.I. Pigment Red 177, an anthraquinone type red pigment, is often used. On the other hand, C.I. Pigment Red 254 with diketopyrolopyrrole structure has attracted attention as a red pigment of an excellent color property. However, a problem exists in the practical use of this pigment because it is difficult to use it in the form of a coating solution.
The inventors have conducted studies, from various angles, on pigments used in a pigment-dispersion photo-sensitive coating solution for colored image formation. As the results, they have obtained following findings. The nature of the colored image is significantly influenced by the amount of a given component, present in the coating solution, which can be extracted from the pigment with an organic solvent, particularly with ethyl acetate. If a pigment rich in the given component is used in a pigment-dispersion photo-sensitive coating solution, the coating solution adversely affects the contrast of a colored image formed therefrom or sometimes produces a colored image poor in transmittance and surface roughness. If a pigment with a smaller content of the given component is selected and used in the coating solution, the resultant coating solution gives a colored image of high quality. Based on these findings, the present invention has been completed.
It is an object of the invention to provide a pigment-dispersion photo-sensitive coating solution selectively employing a pigment with a smaller content of a component adversely affecting the nature of a colored image for giving the colored image excellent in transmittance, surface roughness, contrast and the like. Another objects of the invention are to provide a method for preparation of the pigment-dispersion photo-sensitive coating solution, as well as to provide a method of forming the colored image of a color filter by using the pigment-dispersion photo-sensitive coating solution.
That is, the present invention provides a pigment-dispersion photo-sensitive coating solution which comprises a binder resin, an organic-solvent and a pigment dispersed in the solvent, wherein the combined area of peaks detected at a relative retention ratio in the range of 0.68 to 0.72 based on a retention time of dibutyl phthalate and peaks detected at a relative retention ratio in the range of 1.06 to 1.10 based on a retention time of dibutyl phthalate is not more than 50% of the total area of all peaks when the pigment is extracted by ethyl acetate and the extracts are analyzed by high-speed liquid chromatography using dibutyl phthalate as internal standard.
The present invention also provides a method for producing a pigment-dispersion photo-sensitive coating solution which comprises the step of mixing together a pigment, a binder resin and an organic solvent for dispersing the pigment, wherein the combined area of peaks detected at a relative retention ratio in the range of 0.68 to 0.72 based on a retention time of dibutyl phthalate and peaks detected at a relative retention ratio in the range of 1.06 to 1.10 based on a retention time of dibutyl phthalate is not more than 50% of the total area of all peaks when the pigment is extracted by ethyl acetate and the extracts are analyzed by high-speed liquid chromatography using dibutyl phthalate as internal standard.
The present invention also provides a method for forming a colored-image which comprises the steps of applying a pigment-dispersion photo-sensitive coating solution on a substrate, patterning a resultant coating film by light exposure and developing a colored image, wherein the pigment-dispersion photo-sensitive coating solution comprises a binder resin, an organic-solvent and a main pigment dispersed in the organic-solvent, in which the combined area of peaks detected at a relative retention ratio in the range of 0.68 to 0.72 based on a retention time of dibutyl phthalate and peaks detected at a relative retention ratio in the range of 1.06 to 1.10 based on a retention time of dibutyl phthalate is not more than 50% of the total area of all peaks when the pigment is extracted by ethyl acetate and the extracts are analyzed by high-speed liquid chromatography using dibutyl phthalate as internal standard.